The present invention relates to oscillating apparatus and frequency detecting apparatus, and particularly to voltage controlled oscillating apparatus the frequency of which is variable with an external voltage.
In the conventional voltage controlled oscillators having a basic oscillating circuit using a resistor and a capacitor, or using an inductor and a capacitor, the capacitor is usually implemented with a variable capacitance diode or the like so that the capacitance of the capacitor component of the oscillating circuit is varied with an external voltage, whereby the oscillation frequency determined by a combination of the resistance of the resistor or of the inductance of the inductor and the capacitance of the capacitor is varied.
Further, voltage controlled oscillators have been developed in which an oscillating circuit using a crystal oscillator element or ceramic oscillator element also makes use of a variable capacitance diode so that the overall characteristics are variable to make it possible to control the oscillation frequency more precisely.
Additionally, in recent years, as frequency controlled oscillating apparatus, direct digital synthesizers have also been developed, the frequency of an output of which is numerically controllable. In this apparatus, output waveform data are prepared and stored in a memory in advance, a predetermined constant value is cumulatively added in a cumulative adder in synchronism with an input signal to the apparatus and a data stored at an address determined by a cumulation value is delivered to thereby supplying an output of a frequency different from that of the input signal.